Sorry this is very off topic from the thread, but to answer your question - there is really nothing in Moi that Rhino can't do, except for the n-gon meshing and shelling function. So i use it just for that alone. and it will probably be worth it's price as an add-on utility for many Rhino users. I guess we could break down the Rhino vs. Moi issue to a few simple arguments:

TOOLSET
No comparison. Rhino 4 and Moi are in 2 seperate classes. Rhino is quite obviously the winner...

INTERFACE
Many people seem to love the Moi interface. Whereas, the default Rhino interface can feel a bit intimidating to people who are new to Nurbs modeling. This seems to be where Moi is gaining support. It's very easy to grab it and go. The trick to Rhino is creating your own interface and custom tools (by plug-ins, scripts, or macros). I have recently done this, and now it feels very slick. My work environment is completely submersive. I can work with 100% of my monitor assigned to the grid, and pop-up any of my custom tool palettes (directly under my mouse) with a simple click of a hotkey. So the argument of Rhino having a dinosaur UI is a little bogus, that's the opinion of people who've never explored it's full potential for customization. Also, I have my doubts that Moi's "hands-off" UI will be able to grow along with it's toolbox. IMO the advantage goes to Rhino, although i will probably be stoned to death for saying that in this forum... :)

CONCEPT SKETCHING
For some reason, everybody has overlooked the fact that Rhino does (in fact) have a freeform curve sketching tool. It also has 2 styles of calculators for numerical input. But Moi doesn't require to have have one hand on the keyboard to move objects along the Z-axis. The advantage goes to Moi...

COMPLEX OBJECTS
As it was intended, Moi is very nice for modeling concepts. But it doesn't have the tools to develop complex forms. I'm referring to assemblies of many objects, and also of single complex forms. Advantage to Rhino.

So i guess it depends on what you're modeling. If it's just props for architectural renderings, then Moi is perfectly well-suited. But if you are modeling complex shapes, I would go with Rhino.

jonah